Mechanism for producing internally threaded tubing



Aug. 6, 1957 H. M. WADSWORTH MECHANISM FOR PRODUCING INTERNALLY THREADED TUBING 2 Sheets-Sheet 1 Filed March 10, 1955 Howard 772.1

INVENTOR.

' ATTt NfiY WITNESS:

Aug. 6, 1957 H. M. WADSWORTH 2,801,441

MECHANISM FOR PRODUCING lNTERNALLY THREADED TUBING Filed March 10, 1955 2 Sheets-Sheet 2 I N V EN TOR. WITNESS: lg/011m"! MWUL A DRIVE Y United States Patent MECHANISM FOR PRODUCING INTERNALLY THREADED TUBING Howard M. Wadsworth, Liverpool, N. Y. Application March 10, 1955, Serial No. 493,451

6 Claims. (Cl. 18-14) The present invention relates to a mechanism for producing internally threaded tubing from plastic material and more particularly to form such tubing by a continuous extrusion operation.

There are presently in many arts improvements which could be made if there were an economical source of internally threaded tubing of plastic or ceramic material of length greater than could be practically produced by tapping operations. In the absence of such a product the problems have to be solved by the use of less simple and desirable structure.

It is an object of the present invention to provide a novel instrumentality for continuously extruding tubing to any desired length while forming therein an internal thread of any preferred form and pitch.

It is another object to provide such a device which is readily adaptable to the use of diverse raw materials having various setting and hardening characteristics and qualifications, time and temperature constants, shrinking coefficients, etc. In view of the diverse applicability of the mechanism it is intended that the use of the term plastic throughout the specification shall be considered generic to the range of raw materials above indicated.

Further objects and advantages will be apparent from the following description of one embodiment of the invention, taken in connection with the accompanying drawing which illustrates the structure in a somewhat diagrammatic form, and in which:

Fig. 1 is a vertical substantially mid-sectional view;

Fig. 2 is an end view looking from the right in Fig. 1, certain of the parts being broken away and shown in section; and

Fig. 3 is a sectional view taken substantially on the line 33 of Fig. 1.

In Fig. 1 of the drawing there is illustrated a container or casing 1 having an inlet fitting 2 on which is mounted a positive displacement pump indicated generally by the numeral 3 which is arranged to be connected by a conduit 4 to a source of plastic material from which the tubing is to be formed.

As here illustrated, the pump 3 is in the form of a gear pump comprising two meshing gear-shaped impellers 5 and 6 mounted with close clearance in a casing 7 which provides bearings for the shafts 8 and 9 on which the impellers are mounted. As shown in Fig. 2, the shaft 9 extends outside the casing 7 and is attached at one end to a motor 11 of any suitable power and capacity. On the other side of the casing 7 the shaft 9 is connected by means of a coupling 12 with the driving shaft 13 of a variable speed transmission indicated generally by numeral 14.

As here illustrated, this transmission is in the formof a variable ratio V-belt assemblage of conventional form, the ratio of which may be varied by means of a Control shaft 15 to cause the driving shaft 16 to rotate 2,801,441 Patented Aug. 6, 1957 "ice at any desired ratio to the speed of rotation of the shaft 13 within the scope of adjustment of the device.

I, The container 1 is provided with an outlet spout 17 formed on a plate 18 mounted on the side of the container whereby various sizes and shapes of spouts may be applied interchangeably to the container to produce tubing of various external diameters and contours.

A mandrel 19 is rotatably mounted in a bearing 21 in a plate 22 attached to the side of the container opposite the spout 17, the bearing 21 being coaxial with said spout. The mandrel 19 extends into and partway through the spout 17, and is formed for a portion of its length with an external thread 23 of the desired form and pitch, the diameter of such threaded portion being so chosen as to leave an annular clearance space 24 within the spout appropriate to form the tubing with the desired wall thickness and interior diameter.

It will be understood that various mandrels 19 may be selected at will in order to provide the desired characteristics of the tubing to be formed in cooperation with the spout 17.

Means are provided for rotating the mandrel 19 at such a speed that the conveyer action of the thread on the mandrel due to its rotation is equal to the rate of extrusion of the plastic material from the container by the injector action of the pump 3. As here shown, this means comprises a spiral gear 25 on the driven shaft 16 of transmission 14, which meshes with spiral splines 26 formed on the mandrel 19. It will be understood that other forms of transmission may be used for connecting pump 3 to the mandrel 19, providing only that the relative speeds may be adjusted accurately to secure the desired relationship above set forth, and that such relationship shall thereafter be maintained without substantial variation.

The spout 17 may be provided with heating means indicated diagrammatically at 27 where plastic materials of a thermo-setting character are employed. It will be understood that the interior of the spout may be fluted or of any desired angular cross section, as shown in Fig. 3, particularly where purely rectilinear motion of the extruded tubing is deemed important.

Where appropriate, the portion of the mandrel 19 which protrudes into the spout 17 may be tapered as indicated in order to avoid the possibility of seizing in cases where the extruded material has the quality of shrinking during the setting operation.

In operation, the pump 3 is connected by the conduit 4 to a source of desired plastic material, the selected type and size of spout 17 and mandrel 19 mounted on the container 1, and the motor 11 energized in the direction to cause the pump 3 to force the plastic material into the container 1, and to consequently emerge from the container through the space 24 between the mandrel 19 and the interior surface of the spout 17. At the same time, the speed of rotation of the mandrel 19 is adjusted by means of the shaft 15 of the transmission 14 until an examination of excised sections of the emerging tubing shows that the threads are being formed smoothly without axial pressure in either a forward or backward direction. The process of extrusion is then maintained until the desired quantity of tubing having the particular characteristics has been formed.

It will be understood of course that the usual conditions and procedures appropriate for producing ordinary smooth tubing of the selected material will be carried out in the conventional manner.

Although but one form of the invention has been shown and described in detail, it will be understood that other forms are possible and changes may be made in the design and arrangements of the parts without departing from the spirit of the invention.

I claim:

1.. A device for producing internally threaded tubing from plastic material including a containerl having an inlet, and an outlet spout, a threaded mandrel rotatably mounted coaxially within the spout with an annular space therebetween, means including a continuous flow positive displacement pump for injecting the plastic material into the container and thereby causing it to be extruded through said annular space, and means for rotating the threaded mandrel in predetermined timed relation with the actuation of the pump. f

2. A device as set forth in claim 1 in which the means for rotating the mandrel includes a continuously variable 15 speed-change transmission.

3. A device as set forth in claim 1 in which the means for rotating themandrel includes a variable-speed transmission connected to the pump and the mandrel, in-

cluding further,"means for adjusting the variable-speed 20 transmission to'rotate the mandrel at such speed that the conveyer action of the thread on the mandrel is equal in speed to the rate of extrusion of the plastic through the spout as propelled by the pump.

4. A device as set forth in claim 1 including further, means for heating the outlet spout to set the plastic as it is extruded.

5. A device as set forth in claim 1 in which the interior of the outlet spout is non-circular in cross section to ensure rectilinear movement of the extruded plastic.

6. A device as set forth in claim 1 in which the mandrel is tapered to prevent seizure of the extruded plastic by shrinkage.

References Cited in the file of this patent UNITED STATES PATENTS 121,166 Grifiin Nov. 21, 1871 1,302,484 Stratton et al. Apr. 29, 1919 2,082,720 Rutishauser June 1, 1937 2,566,846 Martin Sept. 4, 1951 2,620,514 .Sampson et al. Dec. 9, 1952 FOREIGN PATENTS I 618,536 Great Britain Feb. 23, 1949 

